Process of treating cellulose to produce vulcanized fiber and the like



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Patented June 24, 1930 UNITED STATES ROBERT R. FULTON, OF 'WILKINSBURG,PENNSYLVANIA, ASSIGNORITO T COMPANY, A CORPORATION OF DELAWARE PATENTOFFICE PROCESS OF TREATING CELLULOSE TO PRODUCE VULCANIZED FIBER AND THELIKE able features of the prior art may beavoided. Y

My invention has for further objects such other operative advantages orresults as may hereinafter be found to obtain.

At the present time, the manufacture of vulcanized fiber is generallyconducted according to the well-known zinc chloride method. According tothis'procesager- Application filed March 16, 1927. Serial No. 175,932.

properties of such solutions with respect to cellulose could be utilizedto gelatinize cellulose. According to the patented process, cellulosicmaterial, such as cotton rag paper, is treated with calcium thiocyanatesolutions of such concentration as to boil at 157 C., and preferablyhaving an acid reaction. The paper is treated with such solution at atemperature of 130 C. for about 30 seconds and is thereafter washed anddried in the usual manner.

The' solutions proposed in the above recited patents are veryconcentrated, being, in fact, so concentrated that they are veryviscous, even at 130 C.,-and solidify at atmospheric temperatures,especially in acid condition.

According to my invention, I treat cotton rag pulp paper, paper madefrom chemical wood pulp, or the like, with a neutral or alkalinesolution of calcium thiocyanate or IIE KOPPERS other thiocyanates ofsuch concentration as to have a boiling point of from about 130 taingrade of cotton rag paper is subjected toabout llOig and preferablycontaining for a few seconds to the action of a 70 Baum solution of zincchloride at a temperature of about 50 C. After this treatment and whilethe paper retains some of the solutions, the paper is rolled upon alarge heated drum and is subjected to a slight perature of the bath andthe time of the treatment must be carefully controlled to prevent theformation of a dark, brittle fiber.

The use of concentrated calcium thiocyanate solutions has been proposedin U. S. Patents Nos. 1,301,652 and 1,333,465, to Clayton et al.,-whodiscovered that the solvent from about 15% to about 30% of formaldehyde.The treatment is carried out at substantially atmospheric temperatures,for example, from about 20 to 40 C. Preferably I do not allow the fiberto remain in the treating bath until gelatinization is complete, but Iremove the fiber from the bath after a short time and allow the treatedfiber to lie flat for a sufficient interval to insure thatgelatinization is carried to a satisfactory degree.

By formaldehyde is meant the usual aqueous solution thereof containingapproximately 40% by volume of CH O and some times known as formalin.

It will be obvious to those skilled in the art that the actual treatmentof the fiber will be subject to' many modifications, such as time oftreatment, concentration of solution, nature and state of cellulosicmaterials used, pressure and the like, according to the nature of thematerials treated or the character of the results desired. However, inorder that my invention may be clearly set comparatively largewmounts fpgample, li

solution of 0a(0NS).3H O and one part of formaldehyde. The reaction ofthe solution is preferably-neutral or slightly alkaline and thetemperature of the solution is maintained at any convenient point withinthe approximate range of from 20 to 40 0..

Higher temperatures are to be avoided. The paper is runthrough" the bathat any speed that permits'thorough wetting without retaining the paperin the-bath for extended intervals. It is then wound, as in priorpractice, upon a large drum, except that the drum is not heated. After asufficient number of layers of the paper have been wound upon the drumto produce a sheet of desired thickness, it is removed, out to desiredsize and allowed to lie fiat for from 30' minutes to several hours inorder to permit gelatinization to take place. It is then pressed, eitherwith or without heat, washed, preferably by the counter-current system,dried and again pressed to form a flat sheet of hard fiber which may bedrilled, machined and polished, as desired.

Although a certain amount of adhesion of the built-up layers orlaminations of fiber may take place prior to the initial pressingoperation, such pressing is desirable to insure that the layers adherethoroughly to each other.

The length of time required for the gelatinization period will varyconsiderably with the nature of the raw material treated and the qualityof the result desired and is best determined by previous experiment forevery condition.

There are many advantages toibegained' b1122%@tiQgcellulcseaccfiding tomy inven-.

tion. It requires no high temperatures, the use of which is alwaysattended with considerable cost. Hot solutions of calcium thiocyanateare much more corrosive, especially in acid condition, than the cold,less concentrated'an'd neutral or alkaline solutions which I prefer.Cold solutions of calcium thiocyanate give rise to less occupationalhazards than hot solutions. Moreover, the presence of formaldehyde in mypreferred solution reduces its corrosive action.

A solution of calcium thiocyanate having a boiling point of 157 0., isery viscous, and, although applied to the paper at 130 0., cools quicklyon the surface of the paper, becoming more viscous, or even crystalline,and rendering its removal from the forming rolls difficult. Much excessmaterial is thus carried to the washing vats.

In my work, I have found that neutral or alkaline solutions of calciumthiocyanate crystallize much less readily than acid solu- I ciumthiocyaia'te which I prefer to use, with a boiling point of about 1340., although viscous, showno tendency to crystallize at .ordinarytemperatures, and the addition of formaldehyde reduces the viscosity ofsuch solution and actually increases the gelatinizing action.

In the process of the aforesaid patents and the present zincchlorideprocess, gelatinization of the cellulose takes place in the treat ingbath. Consequently, the fiber leaving the bath is very tender andrequires extreme care in handling to avoid damage.

In my process, gelatinization does not take place to any substantialextent in the treating bath and the issuing fiber contains much of itsoriginal mechanical strength. The sheets can be removed from the formingroll without diificulty. Furthermore, hard fiber produced by my process.isv not subject to that tendency to blister which at present is thecause of a great deal of annoyance and loss to the manufacturers ofvulcanized fiber. Blistering is caused by the presence in the paper ofspots which have not been gelatinized to the same degree as surroundingareas and, therefore, do not adhere to the adjacent laminations in thefiber sheet. Especially in the zinc chloride process, the extremelybrief period of time which is al-.

lowed for subjecting the paper to the action of the bath makesuniformity of degree of gelatinization very uncertain. A dense area inthe paper being treated, being relatively less absorbent than thesurrounding paper, will be insufficiently gelatinized.

My process has a further advantage with' respect to the presentzincchtoride method in that the fungus growth which occurs in fibertreated according to the prior method,

especially during Warm months, and resulting in the formation of whiteand friable spots, is not incident to the treatment of fiber accordingto my invention. Obviously, fiber made from solutions containin ap-'.material which comprises treating it with a solution of formaldehydeand calcium thiocyanate, the latter not being present in sufficientamount to cause crystallization at 'atmo%heric temperatures.

3. he process of gelatinizing cellulosic material which comprisestreating it with a solution of calcium thiocyanate and formaldehyde atsubstantially atmospheric temperatures, and allowing the treatedmaterial to gelatinize.

4. The recess of producing vulcanized 1 fiber whic comprises treatingpaper with a solution of calcium thiocyanate and formaldehyde, allowingthe treated paper to stand until gelatinized, and converting the therebygelatinized paper into vulcanized 5. The process of producing vulcanizedfiber which comprises treating paper with a solution of calciumthiocyanate of such concentration as to have a boiling point of 20 from130 to 140 0., and containing formaldehyde, allowing the treated paperto gelatinize, and sub ecting it to finishing operations to convert itto vulcanized fiber.

6. The process of producing vulcanized 28 fiber which comprises treatingpaper with a solution composed of substantially 3 parts of an 80%solution of calcium thiocyanate and one art of formaldehyde andconverting the t ereby treated paper into vulcana0 ized fiber.

7. The process of producing vulcanized fiber whic comprises treatingpaper with a solution composed of substantially 3 parts of an 80%solution of calcium tlnocyanate 85 and one part of formaldehyde, and ofneutral or slightly alkalinereaction, and converting the thereby treatedpaper into vulcanized fiber.

In testimony whereof, I have hereunto 4 subscribed my name thisfifteenth(15) day of March 1927.

RGBERT R. FULTON.

